The U.S. may be littered with skyscrapers, but by the end of the year, nearly three-quarters of the world's 100 tallest buildings will be located in Asia and the Middle East.

Currently, the world's tallest building is the Burj Khalifa in Dubai, which stands at 2,722 feet tall. But achieving a building much taller could take a while longer, because although the technology to build the frame may exist, its height will ultimately depends on something else: the height to which its elevators can go.

Elevator technology relies not just on the elevator car, but also cables, pulleys and counterweights which are all very heavy and are currently constraining how high skyscrapers can be built.

Elevator systems have traditionally been tested in tall buildings constructed specifically for this purpose.

But one leading lift manufacturer in Finland has found an alternative and has built the world's tallest lift-testing facility in the world, extending over 1,000 feet below ground, in a disused mine shaft near Helsinki.

The BBC's Rebecca Morelle went to visit the facility and saw them testing new technology -- including double-decker elevators. But she says the ultimate idea is an elevator that does away with all the heavy equipment, instead utilizing electro-magnets to move up and down the shaft.

It would be "the biggest overhaul in elevators since Otis came up with the original design back in the 1850s" and would lift the limits on how high we can build.